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Korean Journal of Metals and Materials > Volume 55(7); 2017 > Article
Korean Journal of Metals and Materials 2017;55(7): 486-491. doi: https://doi.org/10.3365/KJMM.2017.55.7.486
Microstructural Changes of 22Cr-9Mo-3Fe-4Nb Ni-Base Superalloy during Creep
Youngseok Song1, Jinik Suk1, Chung-Yun Kang2
1Materials Development Team, Doosan Heavy Industries & Construction, Changwon 51711, Republic of Korea
2Department of Materials Engineering, Pusan National University, Busan 46287, Republic of Korea
Correspondence  Chung-Yun Kang ,Tel: +82-51-510-2428, Email: kangcy@pusan.ac.kr
Received: 5 December 2016;  Accepted: 14 January 2017.  Published online: 4 July 2017.
ABSTRACT
A new Ni based superalloy is considered as bucket material because of high fatigue resistance with fine grain. However a bucket is usually exposed to high temperature for a long time, so creep rupture tests were conducted to understand the microstructure evolution during creep deformation under various stresses at temperatures of 566, 593, 621, 649 and 670 ℃. The hardness applied to the crept specimen of these alloys increased until the value of LMP reached 25, and decreased while the value of LMP exceeded 25. The microstructure analysis with TEM, SEM and OM were conducted on ruptured specimen to observe the changes of γ″ morphology, carbides, and fracture mode. As a result of investigating microstructural changes and creep properties, it can be concluded that the effect of grain size on creep properties is dominant regardless of the size of γ″.
Keywords: alloys, forging, creep, microstructure, TEM
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